TFT is a thin-film type semiconductor device and is widely applied in the fields such as display technology and integrated circuit technology. In general, in a liquid crystal display (LCD) or an organic light-emitting diode (OLED) display, each pixel unit is driven by a TFT integrated in the rear of the pixel unit, so that image information can be displayed at high speed, high brightness and high contrast. Generally, TFTs may be mainly divided into amorphous silicon (a-Si) TFTs, polycrystalline silicon (poly-Si) TFTs and oxide TFTs according to the composition of TFT semiconductor layers.
As for LCDs and OLEDs, the electron mobility of the poly-Si TFTs may reach 50-200 cm2/Vs, so poly-Si TFT-LCDs have the advantages of higher resolution, rapider response speed, higher aperture opening ratio, etc. In addition, the poly-Si TFT is also a technology platform for developing active matrix organic light-emitting diode (AMOLED) panels. The poly-Si TFT may adopt low working voltage and can reduce the consuming current as a driving backplane of the AMOLED panel.
However, due to the regular arrangement of crystal lattices in the poly-Si TFT, the resistance of electrons in the poly-Si TFT is small, so the serious problem of leakage current can be caused in the off state, and hence the normal use of the poly-Si TFT can be affected. In order to inhibit the leakage current of the TFT, the means of light dope between the source and drain of the TFT is usually adopted. On one hand, the OFF leakage current of pixel switches can be reduced. On the other hand, the phenomenon of hot electron deterioration of peripheral circuits can be improved, and then the reliability can be improved. But in this case, the processing steps of the TFT can be increased; the production time can be increased; and the product yield can be reduced. Moreover, as the critical dimension of lightly doped regions of the source and the drain is difficult to control, the uniformity of products can be reduced.